1. Field of the Invention
The present invention relates to an evaporative fuel supply apparatus, and more particularly to an evaporative fuel supply apparatus that is suitable for supplying evaporative fuel to an internal combustion engine intake system when an internal combustion engine is to be cold-started.
2. Background Art
A conventionally known system disclosed, for instance, by Japanese Patent Laid-Open No. Hei7-229452 stores evaporative fuel, which is generated within a fuel tank, in a canister, and supplies the stored fuel to an intake path during an internal combustion engine operation. When the evaporative fuel is supplied to the intake path, the air-fuel ratio is likely to become disordered. Therefore, the evaporative fuel is generally supplied after internal combustion engine warm-up.
When the temperature is low, liquid fuel is not likely to vaporize. Therefore, the supply of already evaporative fuel to the internal combustion engine is effective for fuel combustibility enhancement. Under these circumstances, the startability of the internal combustion engine can be improved by supplying evaporative fuel to the intake system when the internal combustion engine is to be cold-started.
Under the above circumstances, however, the amount of fuel supply to the internal combustion engine is insufficient so that cylinder combustion may not properly take place during an explosion stroke. Consequently, the intake stroke may begin before completion of cylinder gas combustion. In such a situation, combustion may propagate to the air-fuel mixture existing in the intake path at the beginning of the intake stroke so that backfiring occurs.
The conventional system described above does not assume that evaporative fuel is supplied to the internal combustion engine when it is to be cold-started. Therefore, the conventional system does not assume that backfire may be generated. Consequently, no provision is made in the conventional system in consideration of the influence of backfire.
Including the above-mentioned document, the applicant is aware of the following documents as a related art of the present invention.
[Patent Document 1] Japanese Patent Laid-Open No. Hei7-229452
[Patent Document 2] Japanese Utility Model Laid-open No. Hei3-37270
[Patent Document 3] Japanese Patent Laid-Open No. 2002-21643
However, when backfire occurs, an abnormal pressure arises within the intake path. In the above conventional system, the abnormal pressure propagates to the canister via evaporative fuel supply piping. This pressure propagation decreases the durability of the canister. In this respect, the above conventional system is not always an optimum apparatus for supplying evaporative fuel to the intake system at a cold start.